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The robust non-singular fast terminal sliding mode (NFTSM) controller is adopted in this work to solve the problem of tracking trajectory of a mobile manipulator (MM) suffering from uncertainties. The NFTSM method has the capability to ensure convergence rate and to provide good tracking accuracy and robustness against external perturbations and parameter uncertainties (total disturbances). However, the NFTSM controller needs high discontinuous gain to reject the effect of strong disturbances, which results in vibrations in the steady-state and chattering in the control law. To solve these issues, an extended state observer–based NFTSM technique is proposed for n -degree of freedom (DoF) coupling MM. The proposed method is designed to approximate and compensate in real-time the uncertainties. It also ensures robustness against total disturbances, good convergence rate, and good tracking accuracy. The stability of the proposed control is also verified based on the Lyapunov theory. Experimental works are conducted on a 5-degree-of-freedom (5-DoF) MM where the results obtained demonstrate the effectiveness of the developed technique and prove the stability of the closed-loop system. [ABSTRACT FROM AUTHOR]

This research work focuses on the need to provide a control scheme able to tolerate multiple robotic control challenges related to noisy measurements, unknown disturbances and uncertainties using the joint position measurements only. The proposed control scheme avails the advantages of integrating the Extended State Observer (ESO) with the synergetic control to operate n-DOF robot manipulators. The ESO is known as a powerful tool that can provide the online estimation of the uncertainties, nonlinearities and disturbances to be rejected or compensated by a feedback stabilizer. Correspondingly, implementing ESO in the control scheme makes it work with less knowledge of the system model dynamics and states. On the other hand, the synergetic control is a proper controller that can provide the desired tracking performance, but it has a high dependency on the system model which makes it sensitive to control parameters variation and operating conditions. Hence, combining both techniques in one scheme is a convenient approach to overcoming the shortcoming of each method. The proposed method is tested experimentally on the MICO 4-DOF Kinova robot and its performance is compared to the conventional synergetic control considering three case studies to validate its effectiveness. [ABSTRACT FROM AUTHOR]

This paper deals with the implementation and performance analysis of discrete-time sliding mode (DTSM) current control applied to a seven-level cascade H-bridge converter to track three-phase reference currents for a reactive load. The converter output voltages are synthesized using a modulation scheme based on phase-shifted carrier modulation. Simulation and experimental tests have been added to demonstrate the performance of the proposed controller. At the same time, the effectiveness of the DTSM is verified under transient and steady-state conditions, respectively, by measuring the total harmonic distortion and the mean square error. [ABSTRACT FROM AUTHOR]

This paper develops an inner stator current controller based on an enhanced reaching-law-based discrete-time terminal sliding mode. The problem of tracking stator currents with high accuracy while ensuring the robustness of a six-phase induction motor in the presence of uncertain electrical parameters and unmeasurable states is tackled. The unknown dynamics are approximated by using a time delay estimation method. Then, an enhanced power-reaching law is used to make each stage of the convergence faster. A stability analysis and the system controller's finite-time convergence are demonstrated in detail. Practical work was conducted on an asymmetrical six-phase induction machine to illustrate the developed discrete approach's robustness and effectiveness. [ABSTRACT FROM AUTHOR]

In this paper, a data mining based methodology for process identification from historical data was proposed. Thereon, it considers the phases of process understanding, data collection, data preparation, data modeling, and model evaluation. As some parts of historical data are irrelevant, a data selection step, based on the Gaussian Mixture Model (GMM) clustering algorithm, was considered. Additionally, the methodology includes a data informativity step to study the richness of data. In this regard, the condition number (CN) and the extended CN for ridge regression (RR CN) were used. To evaluate the approach, 2 years of industrial thickener historical data were used. Thereafter, data were prepared and an ARX (Auto-Regressive with eXogenous inputs) model structure was adopted to identify the model. To estimate input delays, Granger causality was used. As for fit criteria, least square regression was tested and compared to ridge regression as a less sensitive method to multicollinearity. The results were then evaluated based on the 20-step ahead prediction and compared to existing methods. In this context, the proposed approach gave the best results with an R2 of 98.11% and 62.70% for 1 and 20-step ahead predictions, respectively. [ABSTRACT FROM AUTHOR]

This article features a novel sliding mode controller for robotic arms using nonlinear model-based switching functions. The new controller is experimentally validated on a 7-DOF exoskeleton arm used for upper-limb rehabilitation applications. The proposed approach features a novel concept using model-based switching functions in the sliding mode controller, which leads to considerable simplifications on the torque control inputs. Compared to conventional linear switching functions, model-based switching functions show substantial control performance improvements on the torque inputs, such as transient constraints reduction and enhanced robustness, while maintaining a very good tracking performance. Moreover, model-based switching functions design ensures a complete decoupling of chattering effect between joint axes. Furthermore, this approach can be combined with existing chattering reduction techniques to ensure proper control of chattering levels on the torque inputs. These advantages make the practical implementation of the model-based switching functions approach particularly desirable for wearable robotics, where smooth movements and high accuracy are important requirements for patients’ comfort and security. [ABSTRACT FROM AUTHOR]

This article tackles the problem of high-accurate tracking of the stator currents of a six-phase induction motor in the presence of unknown dynamics such as unmeasurable rotor currents, parameter variation, and disturbances. Since the good features offered by sliding mode theory motivate the community of researchers on control, a time delay estimation based discrete-time super-twisting controller is proposed. First of all, an outer loop is carried out to regulate the speed and to generate the desired stator currents. Second, the inner loop, based on an indirect rotor field-oriented control, is executed based on the developed approach. The structure of the proposed method allows a precise approximation of the unknown dynamics and an accurate tracking and a fast convergence of the tracking error to a neighbor of zero. The design procedure and the stability analysis are detailed for the stator currents closed-loop system. Experimental tests have been performed on a six-phase induction motor to demonstrate the effectiveness of the developed discrete approach. In addition, the performances obtained are compared to the ones obtained using the discrete-time sliding mode with time delay estimation. The results obtained highlighted the satisfactory stator currents tracking performance in transient conditions and steady state and under different sampling times, parameters mismatch, and load and no-load conditions. [ABSTRACT FROM AUTHOR]

This paper proposes an improved non-singular terminal super-twisting control for the problem of position and attitude tracking of quadrotor systems suffering from uncertainties and disturbances. The super-twisting algorithm is a second-order sliding mode known to be a very effective control used to provide high precision and less chattering for uncertain nonlinear electromechanical systems. The proposed method is based on a non-singular terminal sliding surface with new exponent that solves the problem of singularity. The design procedure and the stability analysis of the closed-loop system using Lyapunov theory are detailed for the considered system. Finally, the proposed control scheme is tested in simulations and by experiments on the parrot-rolling spider quadrotor. Moreover, a comparison is made with the standard super-twisting algorithm in the simulation part. The results obtained show adequate performance in trajectory tracking and chattering reduction. [ABSTRACT FROM AUTHOR]

This study deals with the problem of controlling rotor speed and stator currents of an asymmetrical six‐phase induction machine with uncertain dynamics, disturbances, and unmeasurable rotor currents and proposes a robust non‐linear variable structure controller. First of all, an outer control loop based on a proportional–integral regulator is performed to control the rotor speed and to construct the desired stator current references. Then, the inner loop is performed based on the proposed method that combines the time delay estimation method and discrete sliding mode control based on exponential reaching law. This structure allows an accurate and simple estimation of uncertainties and rotor currents, a high‐tracking precision, a convergence of the stator currents to their known desired references in finite‐time and chattering reduction. The design procedure is detailed step by step and the stability analysis and the convergence time are established for the current closed‐loop system. Experimental work was carried out on an asymmetrical six‐phase induction motor drive to show the effectiveness and performance of the proposed robust non‐linear discrete method. The results obtained highlighted the good tracking performance of the stator currents. [ABSTRACT FROM AUTHOR]

In this manuscript, the high-accuracy stator currents tracking issue is considered for a six-phase induction motor subject to external perturbations and uncertainties due to unmeasurable rotor currents and electrical parameter variations. To achieve the control goals, the common two-cascade controllers structure is required for this type of motor. The first controller in the outer loop consists of a proportional integral to regulate the speed. Then, the second is the proposed inner nonlinear stator currents controller based on a robust discrete-time terminal super-twisting algorithm supported by the time-delay estimation method. For the design procedure, the discrete-time stator currents dynamics are derived; for example, the vector of the matched perturbations and unmeasurable rotor currents are specified to simplify the estimation. A detailed stability analysis of the closed-loop error dynamics using Lyapunov theory is given. Finally, a real asymmetrical six-phase induction motor is used to implement in real-time the developed method and to illustrate its effectiveness and robustness. The results obtained reveal a satisfactory stator currents tracking in steady state and transient conditions and under variation in the magnetizing inductance. Moreover, a comparative study with an existing method in steady state for two different rotor speeds is presented to show the superiority of the proposed discrete-time technique. [ABSTRACT FROM AUTHOR]